-LRB- CNN -RRB- -- Coinciding with this season 's flu outbreak is an upsurge of another illness that can be dangerous , even deadly , especially for infants : respiratory syncytial virus -LRB- RSV -RRB- .

While most parents are familiar with the flu , many have never heard of RSV . It 's the same virus that is the leading cause of the common cold -- and infects almost all children by age 2 .

`` The vast majority of kids who get RSV just have cold symptoms and get better , '' says Dr. Robert Wiskind , Georgia president of the American Academy of Pediatrics . `` A minority of them develop bronchiolitis -LRB- an inflammation of tiny air passages in the lungs specific to babies and young children -RRB- -- and a very small percentage have significant problems . ''

When RSV attacks the lungs , it is particularly dangerous for newborns and babies born prematurely . Pneumonia and other bronchial complications can set in quickly .

RSV and other winter worries

It is an age-old , recurring illness -- most adults have been exposed countless times . Subsequent RSV infections usually are not as severe as the first .

RSV , which generally circulates from late fall into the early spring , is out there with a myriad of other stuff floating around right now : Human metapneumovirus -LRB- hMPV -RRB- , adenovirus and parainfluenza , all common respiratory viruses , and pertussis , the bacterial disease that causes whooping cough . Since patients often are treated without being tested , it 's hard to know what 's what .

`` Just in general , when we look at cough and respiratory symptoms , there 's a lot of overlap , '' said Dr. Susan Gerber , an epidemiologist at the Centers for Disease Control and Prevention -LRB- CDC -RRB- . `` A lot of times , unless there is rigorous laboratory testing , you may not know the cause . ''

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With no official reporting of RSV , year-to-year comparisons are difficult to gauge except to say spikes are typical this time of year .

In Boston , a city hit hard by the flu , Massachusetts General Hospital has more than 175 cases of RSV on the record so far this season . At the three pediatric hospitals that make up Children 's Heathcare of Atlanta , some 545 youngsters have been treated for RSV since the beginning of December , according to the group 's clinical microbiologist , Dr. Robert Jerris .

Katie Dearborn 's 2-month-old son , Cooper , recently spent three days in an Atlanta hospital . `` I brought him in because he was wheezing and coughing , '' she says . `` He had just learned to smile -- and he stopped smiling . He just looked sad . ''

Wiskind advises , `` You are the best judge of your child -- if it does n't seem right to you , you should bring them in . ''

Serious symptoms

Parents should seek immediate medical attention if their children have any of these symptoms :

-- High fever

-- Severe cough

-- Wheezing

-- Difficulty breathing

-- Bluish-colored skin on the lips and nail beds

RSV spreads much like the flu -- exposure from others who are coughing or sneezing and by direct skin-to-skin contact . The virus can live for hours on contaminated surfaces such as toys . It is most contagious during first few days of infection .

Treatment

Milder coldlike symptoms can be alleviated with proper humidity , over-the-counter pain relievers , nasal drops and extra fluids .

Hospital treatment for serious cases may include antibiotics , IV fluids and humidified oxygen . Medications delivered in a fine mist can relieve wheezing .

Cooper Dearborn tested positive for RSV but responded quickly following a procedure to clear his lungs of congestion .

`` It was a little scary . I 'm grateful to all of the nurses and doctors who kept me calm , '' his mother says .

Prevention

Parents should take the same precautions for all respiratory illnesses : wash hands , limit contact with others who are sick , do n't smoke and keep surfaces clean .

For babies at highest risk -- those born prematurely , with congenital heart or lung disease -- there is one medication to help ward it off : Doctors may administer a series of injections -LRB- Palivizumab -RRB- as a protective measure . But it 's an expensive treatment not indicated for general use .

Preventive actions do pay off , Wiskind says .

`` The number of fatalities from RSV has dropped significantly in recent years . ''

There currently is no vaccine for RSV . But `` we are hopeful , '' Gerber says . `` There are multiple candidates for a vaccine in development . ''

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RSV is caused by the same virus that 's the leading cause of the common cold

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Most children recover without complications , but some have `` significant problems ''

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Serious cases may require hospitalization